The pedal mechanism of a base drum as shown in FIG. 1, is generally comprised of two upright supports upstanding from a base frame to hold a revolving shaft in a horizontal position by bearings, a flywheel mounted around the revolving shaft, a pedal having one end hinged to the base frame and an opposite end connected to the flywheel by a chain, a beater holder fixed to the flywheel to hold a beater by a screw. As the pedal is pressed by the foot, the chain is pulled downward to turn the flywheel, causing the beater to hit the drum. The amplitude of the beater is controlled by a cam mechanism. The cam mechanism is comprised of an inner cam fixed to the revolving shaft, an outer cam engaged with the inner cam and coupled with a hanging ring, a spring having a top end suspended from the hanging ring and a bottom end fastened to the locating member at an outer side by one upright support. The spring is provided to return the beater and the pedal back to their former positions after each strike. The procedure to adjust the amplitude of the beater is done by loosening the cam mechanism, then turning the revolving shaft to change the angular position of the heater holder. When adjusted, the cam mechanism is fastened tight again. As the angular position of the beater holder is adjusted, the elevation of the free end of the pedal is relatively adjusted. When the free end of the pedal is lifted higher, more effort should be employed to the pedal to pull the chain and turn the flywheel. Due to the limitation of the chain, the adjustable range of the amplitude of the beater is limited, and therefore the quality of the drum cannot be fully carried out.
In order to eliminate the aforesaid drawbacks, the present invention invented a beater amplitude adjustment device for the base drum pedal mechanism of a base drum and applied for a patent under U.S. patent application Ser. No. 08/120,513. This adjustment device is comprised of a beater holder mounted around the revolving shaft of the pedal mechanism of a base drum to hold a beater, and a locating device made of a split cylinder and fastened around the revolving shaft to retain the beater holder in position. The beater holder consists of two opposing parts connected together around the locating device by screw bolts. The angular position of the beater is adjusted by loosening the screw bolts, then turning the beater holder to the desired angular position around the locating device, and then fastening tight the screw bolts again.